Ankle arthritis is common following a traumatic injury such as an ankle fracture, ligament injury or failed open reduction internal fixation. Arthritis is also seen in patients with rheumatoid arthritis and in diabetic patients with Charcot arthropathy. In comparison to most patients affected by hip and knee arthritis, ankle arthritis patients are usually younger and have often had prior ankle surgery. The treatment goal is to provide pain relief. Currently, patients with ankle arthritis are presented with either fusion or arthroplasty as surgical options.
A fusion, or arthrodesis, is an effective solution for pain resulting from ankle arthritis and has been the historical gold standard for treatment. An arthrodesis is currently the recommended option for patients with diabetic Charcot arthropathy, post traumatic patients with poor bone stock, and in the young active patient with arthritis. Arthrodesis is also a surgical option following failed ankle arthroplasty. An ankle arthroplasty is another possible solution for ankle arthritis, and often involves a replacement of the distal tibia and/or a portion of the talus. However, problems exist with some of the current systems for ankle arthrodesis and arthroplasty.
Current systems that perform ankle fusion fixation have certain disadvantages. First, some cannulated screws have been complicated by hardware failure prior to complete fusion, as well as lack of adequate compression across the fusion site. Depending on the orientation of screw insertion, the screws may not restrict motion in the plane of motion of the joint and therefore increase the likelihood of development of nonunion. Second, some plate systems are often able to accommodate deformity in only one plane, and also can cause prominence that leads to postoperative skin irritation. Third, some hindfoot fusion nails have been inserted retrograde to treat ankle arthritis. Insertion of the retrograde nail will sacrifice the subtalar joint even though the joint may not be affected by arthritis. Current retrograde fusion nails are not designed to specifically fuse the posterior facet of the subtalar joint. A common complication of current retrograde systems involves a nonunion of the posterior facet joint because they do not specifically fuse this area with the fusion nail. The plantar skin incision that is required for the retrograde nail has been associated with wound complications and injury to the plantar branch of the tibial nerve. Many of these forms of ankle arthrodesis require an 8 to 12 week period of strict non weight bearing to ensure fusion, and patient compliance with non weight bearing is often difficult to achieve.
The current generation of ankle arthroplasty systems presents disadvantages resulting in poor patient outcomes. Current ankle arthroplasty may not be a viable option for patients who have poor bone stock. These patients include those who have undergone past operative procedures for fractures and diabetic patients with Charcot arthropathy. Poor bone stock in the distal tibia and talus can result in implant malposition and failure. Second, traditional ankle arthroplasty may not be an ideal option for the young and active patient because of the risk of increased wear and early implant failure. Third, many current total ankle arthroplasty systems require resection of a significant amount of bone from both the tibia and talus in order to create a space for insertion of the implants. These large bone cuts can create a large void to fill if the ankle replacement fails. A fusion following an arthroplasty with large bone cuts is often complicated by an increased rate of nonunion.
Therefore, the need exists for improved ankle arthrodesis and arthroplasty systems. An arthrodesis system which provides improved compression across the fusion site and/or structural bone support may result in improved long-term fusion and pain relief. An arthrodesis or arthroplasty system which relies on anchoring or fixation on strong outer cortical bone instead of compromised bone stock may provide an increased rate of union, or longer lasting wear, respectively. An arthroplasty system which requires minimal resection may result in enhanced comfort and mobility. An arthroplasty convertible to a fusion system with minimal disturbance of surrounding tissues may result in better union following the fusion.